class Robot:
    population = 0
    
    def __init__(self,name):
        self.name = name
        print("(Initializing {})".format(self.name))
        
        Robot.population += 1
    def die(self):
        print("{} is being destroyed!".format(self.name))
        
        Robot.population -= 1
        
        if Robot.population == 0:
            print("{} was the last one.".format(self.name))
        else:
            print("There are still {:d} robots working.".format(Robot.population))
    
    def say_hi(self):
        print("Greetings, my masters call me {}".format(self.name))
    
    @classmethod
    def how_many(cls):
        print("We have {:d} robots.".format(cls.population))

droid1 = Robot("R2-D2")
droid1.say_hi()
Robot.how_many

droid2 = Robot("C-3PO")
droid2.say_hi()
Robot.how_many

print("\nRobots can do some work here.\n")

print("Robots havefinished their work. So let's destroy them.")
droid1.die
droid2.die

Robot.how_many()